This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Mosquitoes are hosts to a number of pathogens including parasites, bacteria, viruses, and fungi, and were responsible for more human disease and death in the 17th through 20th centuries than all other causes combined. Today malaria alone infects 500 million people worldwide, and kills at least two million people each year. It is critical to have a detailed understanding of the biological processes crucial for mosquito survival in order to develop effective and specific control methods. One process which has long been overlooked in anopheline mosquitoes is ion regulation, a key organ of which is the rectum. I sought to characterize the functions of the newly identified cell types (DAR and non-DAR cells) of the larval anopheline rectum using the self-referencing ion-selective electrode technique. The Biocurrents Research Center was an invaluable resource for this project providing both the equipment and the expertise necessary for my research. To obtain a better understanding of the functions of the DAR and non-DAR cells of the anopheline rectum, I measured K+ and H+ ion flux at the basal membrane of the rectal cells of Anopheles albimanus mosquito larvae reared in either 2% (fresh) or 50% artificial sea water. K+ ion flux was very low and I was unable to draw definitive conclusions because of my inability to distinguish actual flux from background. However, I found a consistent H+ ion flux pattern that seemed to be independent of rearing salinity. I found a strong H+ ion efflux at the DAR cells and a clear drop in flux at the non-DAR cells. Additionally, acetazolamide (a carbonic anhydrase inhibitor) inhibited DAR cell flux, but not non-DAR cell flux. This supports previous data that carbonic anhydrase differentially localizes to the DAR cells of the anopheline rectum. Data from other pharmacological blockers implicates V-ATPase in the ion efflux and excludes K+/H+ transporters. Combining this physiological data with molecular and immunological techniques can afford us a clearer picture of ion regulation in anopheline larvae.